1. Field of the Invention
The present invention relates to adaptive optics and, more specifically, to micro-electromechanical systems (MEMS) for implementing adaptive optics.
2. Description of the Related Art
Adaptive optics is a field of optics dedicated to the improvement of optical signals using information about signal distortions introduced by the environment in which the optical signals propagate. An excellent introductory text on the subject is given in “Principles of Adaptive Optics” by R. K. Tyson, Academic Press, San Diego, 1991, the teachings of which are incorporated herein by reference.
A representative example of an adaptive optical element is a deformable mirror driven by a wavefront sensor and configured to compensate for atmospheric distortions that affect telescope images. Small naturally occurring variations in temperature (˜1° C.) in the atmosphere cause random turbulent motion of the air and give rise to changes in the atmospheric density and, hence, to the index of refraction. The cumulative effect of these changes along the beam propagation path may lead to beam wandering and spreading and to beam intensity fluctuations, each of which degrades image quality. The wavefront sensor is a device that measures the distortions introduced in the atmosphere and generates feedback for the deformable mirror. Based on the feedback, the mirror is deformed such that the beam distortions are significantly reduced, thus improving the image quality.
A typical deformable mirror of the prior art is a deformable membrane, the shape of which is controlled by an array of underlying electrostatic actuators, e.g., electrodes. However, because each electrode affects the shape of the entire membrane, the shape of the membrane is difficult to control. In addition, the maximum deformation amplitude for a typical membrane mirror is on the order of 1 μm, which puts a corresponding limit on the range of wavefront distortions correctable with that membrane mirror. As a result, prior art membrane mirrors can primarily be used for correcting only relatively small distortions.